An urethane coating compositions which have polyisocyanate as the hardening agent have excellent chemical resistance and good flexibility and the like and are widely used as a coating material for cars, building interiors and exteriors, household appliances, and the like. Furthermore, since coatings obtained from polyisocyanates which are derived from aliphatic diisocyanates have excellent coating physical properties such as non-yellowing and weather-resistance, they are widely used.
In particular, isocyanurate type polyisocyanates which contain an isocyanurate group are known to have excellent coating physical properties such as weather-resistance (Patent document 1).
Furthermore, with the isocyanurate type polyisocyanate disclosed in Patent document 2, compared to the prior art, the cross-linking performance and the drying performance of the coating are equivalent, and in addition, it has an excellent low viscosity, compatibility with polyol, and solubility in low polarity solvents. However, further solubility in low polarity solvents has been sought.
In addition, isocyanurate type polyisocyanates are more stable than polyisocyanates having other structures. During storage, there is only slight increase in diisocyanate monomer concentration, but further suppression of the increase of the concentration has been sought.
With polyisocyanate mixtures disclosed in Patent document 3, in which a monoisocyanurate group and a monoallophanate group are present in a prescribed mol ratio, the mixtures have even lower viscosity, excellent compatibility with polyol and solubility in low polarity solvents. However, the increase of the allophanate group has in some cases reduced the cross-linking of polyisocyanate, and reduced the drying performance as well as the weather-resistance of the coating.
Patent Document 1: JP-A-55-38380
Patent Document 2: JP-B-6-62913
Patent Document 3: JP-A-5-70444
Patent Document 4: JP-A-61-151179